1. Field of the Invention
The invention relates to a method and apparatus for verifying the position of a target to be treated by a radiation therapy device operating in accordance with a radiation therapy plan.
2. Description of Related Art
Modern day radiation therapy of cancerous tumors has two goals: eradication of the tumor and avoidance of damage to healthy tissue and organs present near the tumor. It is believed that a vast majority of tumors can be eradicated completely if a sufficient radiation dose is delivered to the tumor volume; however, complications may result from use of the necessary effective radiation dose, due to damage to healthy tissue which surrounds the tumor, or to other healthy body organs located close to the tumor. The goal of radiation therapy is to confine the delivered radiation dose to only the tumor volume defined by the outer surface of the tumor, while minimizing the dose of radiation to surrounding healthy tissue or adjacent healthy organs or structures.
Radiation therapy treatment typically uses a radiation delivery device such as a linear accelerator, or other radiation producing source, to treat the tumor. The radiation delivery device typically has a radiation beam source which is positioned about the patient and directs the radiation beam toward the tumor to be treated. Various types of devices have been proposed to conform the shape of the radiation treatment beam to follow the spatial contour of the tumor as seen by the radiation treatment beam, from a linear accelerator, as it passes through the patient's body into the tumor, during rotation of the radiation beam source, which is mounted on a rotatable gantry of the linear accelerator. Multileaf collimators, which have multiple leaf, or finger, projections which can be moved individually into and out of the path of the radiation beam, can be so programmed, and are examples of such devices. Various types of radiation treatment planning systems can create a radiation treatment plan, which when implemented will deliver a specified dose of radiation shaped to conform to the target, or tumor, volume, while limiting the radiation dose delivered to sensitive surrounding healthy tissue or adjacent healthy organs or structures.
A basic problem in radiation therapy is knowing where the target, or tumor, is located at the time the radiation therapy treatment is occurring. The use of the term "target" is intended to include not only a tumor or a body organ, or portion thereof, to be treated, but also an organ, sensitive body structure, or portion thereof to be avoided in the radiation therapy treatment. It is assumed that the patient's position and the target's position within the patient will be grossly, or nominally, the same at the time of radiation treatment, as it was at the time the radiation treatment plan was created. If the position of the target is not the same as it was at the time the treatment plan was determined, the dose of radiation may not be delivered to the correct location within the patient's body. Since patients are not always positioned properly on the treatment table of the radiation therapy device, which may be a linear accelerator or a cobalt unit, and since organs of a patient may move within the patient from day to day, the target may not be positioned at the exact location where the radiation therapy plan has assumed it would be located. Thus, present day radiation therapy plans typically regard the target to be treated to occupy a space in the patient's body which is larger than it really occupies, in order to insure that the target to be treated regardless of its location within the patient's body, falls within the volume of tissue which receives the desired radiation treatment dose. A disadvantage of such conventional radiation therapy plans is that there is a major concern associated with increasing the volume of tissue which is treated, to insure that the actual target to be treated receives the desired dose of radiation. Because some healthy tissue surrounds the target to be treated, or healthy organs, or sensitive structures, lie adjacent to the target to be treated, delivering the maximum desired radiation dose to this larger volume of tissue may occur and increase risk of damaging healthy tissue, healthy organs, or sensitive structures. This increased risk may cause oncologists to deliver a smaller radiation dose to the larger treatment volume, which is safer for the healthy tissue, with the potential disadvantage of underdosing the target to be treated.
Therefore, the art has sought a method and apparatus for verifying the position of a target, within a body of a patient for use in a radiation treatment plan, which: verifies that the position of the target in the radiation treatment plan is positioned to conform to the position of the target used in the radiation treatment plan; and prevents healthy tissue surrounding the target, or healthy organs and sensitive structures from being exposed to an undesired amount of radiation.